Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a "waterworld." On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. Here we explore how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady state after similar to 2 Gyr. Using these steady. states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (greater than or similar to 0.3% of total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady. state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.

In anticipation of improved observational data for Jupiter's gravitational field, from the Juno spacecraft, we predict the static tidal response for a variety of Jupiter interior models based on ab initio computer simulations of hydrogen-helium mixtures. We calculate hydrostatic-equilibrium gravity terms, using the non-perturbative concentric Maclaurin Spheroid method that eliminates lengthy expansions used in the theory of figures. Our method captures terms arising from the coupled tidal and rotational perturbations, which we find to be important for a rapidly rotating planet like Jupiter. Our predicted static tidal Love number, k(2) = 0.5900, is similar to 10% larger than previous estimates. The value is, as expected, highly correlated with the zonal harmonic coefficient J(2), and is thus nearly constant when plausible changes are made to the interior structure while holding J(2) fixed at the observed value. We note that the predicted static k(2) might change, due to Jupiter's dynamical response to the Galilean moons, and find reasons to argue that the change may be detectable-although we do not present here a theory of dynamical tides for highly oblate Jovian planets. An accurate model of Jupiter's tidal response will be essential for interpreting Juno observations and identifying tidal signals from effects of other interior dynamics of Jupiter's gravitational field.

Hot Jupiters receive strong stellar irradiation, producing equilibrium temperatures of 1000-2500 K. Incoming irradiation directly heats just their thin outer layer, down to pressures of similar to 0.1 bars. In standard irradiated evolution models of hot Jupiters, predicted transit radii are too small. Previous studies have shown that deeper heating-at a small fraction of the heating rate from irradiation-can explain observed radii. Here we present a suite of evolution models for HD 209458b, where we systematically vary both the depth and intensity of internal heating, without specifying the uncertain heating mechanism(s). Our models start with a hot, high-entropy planet whose radius decreases as the convective interior cools. The applied heating suppresses this cooling. We find that very shallow heating-at pressures of 1-10 bars-does not significantly suppress cooling, unless the total heating rate is greater than or similar to 10% of the incident stellar power. Deeper heating, at 100 bars, requires heating at only 1% of the stellar irradiation to explain the observed transit radius of 1.4R(Jup) after 5 Gyr of cooling. In general, more intense and deeper heating results in larger hot-Jupiter radii. Surprisingly, we find that heat deposited at 10(4) bars-which is exterior to approximate to 99% of the planet's mass-suppresses planetary cooling as effectively as heating at the center. In summary, we find that relatively shallow heating is required to explain the radii of most hot Jupiters, provided that this heat is applied early and persists throughout their evolution.